[BEIJING] Scientists have sequenced the genome of a
genetically modified (GM) papaya, a step that could benefit both
cultivation of the fruit and the understanding of fruit tree genomics.

As the first GM virus-resistant fruit tree to be sequenced,
the researchers also hope it will further the understanding of GM
genomes and the effects of inserted genes.

Led by Wang Lei at China-based Nankai University and Ray Ming
from the US-based University of Illinois at Urbana-Champaign,
researchers from 22 US and Chinese institutions published the draft
genome in Nature today (24 April).

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Rich in provitamin A, vitamin C, potassium, magnesium and
fibre, papaya is one of the most nutritious cultivated fruits. It is
grown across the globe's tropical regions and recommended for
preventing vitamin A deficiency in children.

The researchers sequenced over 90 per cent of papaya's genome.
They found that it has significantly fewer genes than other sequenced
flowering plants, and that the plant has not experienced major genetic
change across its genome in the last 72 million years.

When compared with other flowering plants, the researchers
also found genetic changes associated with enhanced fruit production,
adaptation to tropical day lengths and attracting seed dispersal agents
such as animals.

The 'SunUp' papaya used by the scientists contains randomly
inserted genes to give it immunity to the papaya ringspot virus, which
reduces papaya yields and fruit quality.

Lai Zhongxiong, director of the Institute of Subtropical
Fruits at Fujian University of Agriculture and Forestry, welcomes the
study, saying it could offer information on cultivating papaya
varieties with diversified traits such as higher yields and tolerance
in extreme environments.

"More importantly, so far most genetic insertions in GM plant
breeding take place randomly. The method used in this study may help
researchers better understand the role of the inserted genes in the GM
crops, easing safety concerns on them," Lai told SciDev.Net.

The draft genome sequence has been added to the GenBank database and is freely available to researchers worldwide.